Lithium-ion batteries are an increasingly important power source for small and large scale energy storage applications, including portable devices and vehicles. However, their cost of production remains high, they can have significant degradation over the product life-cycle and there have been some catastrophic failures. Improvements in the battery's manufacturing process can provide cost-saving, improve life-cycle performance and enhance safety. Many battery technologies use a similar manufacturing process that involves coating of anode and cathode materials on a metallic film; thus, improvements in the manufacturing process could affect a wide range of current and future battery chemistries.
Significant flaws in a battery can sometimes be detected immediately after manufacturing during the conditioning period and initial testing of the battery, where the cost is just the lost time and materials for that one battery. More problematic are minor flaws that can go undetected, but overtime lead to a loss of capacity that can result in warranty returns and may in some cases have long term safety consequences. For example, if the Li-ion batteries in a PHEV do not meet the life performance warranty, the whole car which is built around the battery may have to be returned with devastating financial impact. In addition to a loss in capacity, flaws in electrode materials can lead to imbalances of charge states upon charging and discharging and can lead to some cells overcharging and overdischarging, leading to potential safety concerns associated with unsafe voltage regimes. Unsafe voltage regimes can be characterized by formation of gases, and if the battery is somehow damaged to expose the cells to moisture and oxygen, can cause explosive reactions. Thus, manufacturing integrity is important not only for warranty repairs but also for the well being of consumers of the batteries.
In order to mitigate some warranty and safety concerns, Li-ion batteries are currently only used at approximately 30% of full capacity. If the manufacturing process could be improved so that just 40% of full capacity could be used, this would result in a ⅓ increase in the effectiveness of these battery using existing chemistry. Considering the tens of billions of dollars in current production of large format Li-ion batteries, even modest improvement in manufacturing technology can have good payoff.
What is needed are improvements in the processes used to detect manufacturing flaws before the battery is assembled. Various embodiments of the present invention do this in novel and unobvious ways.